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Adjustment of the sensor calibration "Concentration_Offset" [ppm] and "Concentration_Span" [ppm] allows
correcting the measured values with the linear function:
C
In practice, the correction values are entered: e.g. if the measured offset is -1 ppm, 1 has to be entered under
Customer offset, and if the slope for the span (or "gain") is too steep by 5%, enter 0.95 under Customer Span
to correct the slope. Upon "OK" the corrected values will be saved in the firmware of the sensor and are also
used to correct the analog output.
It is best to proceed step-wise: first, correct the offset value at zero concentration and then correct for span at
the application concentration (e.g. 50 ppm).
To go back to the standard calibration, the following values need to be entered:
Please note that if you have a two gases system like CH4/CO2 or CH4/C2H6 you also can correct
offset and span for the 2
2.6 Zeroing and Purging
Before starting a measurement, it is generally recommended to perform a zeroing (without target gas in the
flow) and adjust the offset value accordingly. This operation is done to adapt the reading of device to the actual
operation conditions (pressure, temperature, humidity ...).
In case of air being used for the zeroing, make sure your device is not measuring CO2 as air may contain few
hundreds ppm of CO2 that will lead to a wrong value for the offset.
2.7 Gas supply
The piping system surrounding the device is important. Leaks in the piping system can falsify the results. It is
therefore recommended to check the system for leaks. The use of correct fittings and sealing helps to avoid
leaks. Use standard pressure reduction equipment on gas bottles. Maximum flow is 3 l/min and minimum flow
0.1 l/min.
When no gas tubes are connected to the sensor module or the device is on stock the gas connector
plugs should be used to prevent the gas cell from contamination.
When measuring potentially dangerous concentrations of toxic gases (CH4
the exhaust of the device to a safe area. Improper venting of the exhaust may cause serious injury.
2.8 Adjusting firmware integration time (T90)
Depending on the application the device sends one or two values per second. The integration time can be
increased for applications where longer measurement periods can be accepted. This reduces the noise of the
measurement but increases the reaction time. If the integration time is increased, the measurement values sent
by the device represent a moving average. The averaging used is an exponential weighted average (1-pole
filter
similar to an RC filter, for further information check LGD FAQ document). The value set in the user interface
will be saved in the firmware of the device and thus is available even after disconnecting the device.
Min value:
0 s (no Integration)
Max value:
600 s (limited to this value)
The integration on the concentration values is directly linked with the analog output. The measured
concentration is directly transferred into an analog value.
The values for integration time can be set in the Customer Frontend in the menu "Settings" -> "Sensor
Parameter", changed parameter can be saved in EEPROM with "OK" button.
Axetris AG
LGD Compact Operating & Integration Instructions; Rev. D
(
C
Offset
)
new
meas
.
nd
gas concentration.
or
y
Span
(
x
b
)
m
Offset = 0 / Span = 1
C2H2, etc.), properly vent
,
IIR
22/46
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